Metabolic stability, receptor binding, cAMP generation, insulin secretion and antihyperglycaemic activity of novel N-terminal Glu(9)-substituted analogues of glucagon-like peptide-1

Glucagonlike peptide-1(7 36)amide (GLP-1) is an incretin hormone with therapeutic potential for type 2 diabetes. Rapid removal of the Nterminal dipeptide, His7-Ala8, by the ubiquitous enzyme dipeptidyl peptidase IV (DPP IV) curtails the biological activity of GLP-1. Chemical modifications or substitutions of GLP-1 at His7 or Ala8 improve resistance to DPPIV action, but this often reduces potency. Little attention has focused on the metabolic stability and functional activity of GLP-1 analogues with amino acid substitution at Glu9, adjacent to the DPP IV cleavage site. We generated three novel Glu9-substituted GLP-1 analogues, (Pro9)GLP-1, (Phe9)GLP-1 and (Tyr9)GLP-1 and show for the first time that Glu9 of GLP-1 is important in DPP IV degradation, since replacing this amino acid, particularly with proline, substantially reduced susceptibility to degradation. All three novel GLP-1 analogues showed similar or slightly enhanced insulinotropic activity compared with native GLP-1 despite a moderate 4 10-fold reduction in receptor binding and cAMP generation. In addition, (Pro9)GLP 1 showed significant ability to moderate the plasma glucose excursion and increase circulating insulin concentrations in severely insulin resistant obese diabetic (ob/ob) mice. These observations indicate the importance of Glu9 for the biological activity of GLP-1 and susceptibility to DPP IVmediated degradation.

Degradation, receptor binding, insulin secreting and antihyperglycaemic actions of palmitate-derivatised native and Ala(8)-substituted GLP-1 analogues

The hormone glucagonlike peptide-1(736)amide (GLP-1) is released in response to ingested nutrients and acts to promote glucosedependent insulin secretion ensuring efficient postprandial glucose homeostasis. Unfortunately, the beneficial actions of GLP-1 which give this hormone many of the desirable properties of an antidiabetic drug are short lived due to degradation by dipeptidylpeptidase IV (DPP IV) and rapid clearance by renal filtration. In this study we have attempted to extend GLP-1 action through the attachment of palmitoyl moieties to the epsilon-amino group in the side chain of the Lys(26) residue and to combine this modification with substitutions of the Ala(8) residue, namely Val or aminobutyric acid (Abu). In contrast to native GLP-1, which was rapidly degraded, [Lys(pal)(26)]GLP-1, [Abu(8),Lys(pal)(26)]GLP-1 and [Val(8),Lys(pal)(26)]GLP-1 all exhibited profound stability during 12 h incubations with DPP IV and human plasma. Receptor binding affinity and the ability to increase cyclic AMP in the clonal beta-cell line BRIN-BD11 were decreased by 86- to 167-fold and 15- to 62-fold, respectively compared with native GLP-1. However, insulin secretory potency tested using BRIN-BD11 cells was similar, or in the case of [Val(8),Lys(pal)(26)]GLP-1 enhanced. Furthermore, when administered in vivo together with glucose to diabetic (ob/ob) mice, [Lys(pal)(26)]GLP-1, [Abu(8),Lys(pal)(26)]GLP-1 and [Val8,Lys(pal)26]GLP-1 did not demonstrate acute glucoselowering or insulinotropic activity as observed with native GLP-1. These studies support the potential usefulness of fatty acid linked analogues of GLP-1 but indicate the importance of chain length for peptide kinetics and bioavailability.

Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/ cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO 2, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO 2 is typically 18. On silicon, best results are obtained when the HfO 2 is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO 2 deposition, using an in-situ nitrogen plasma treatment. © Springer Science+Business Media, LLC 2007.

Germanium on Sapphire By Wafer Bonding

This paper describes the creation of a germanium on sapphire platform, via wafer bonding technology, for system-on-a-chip applications. Similar thermal coefficients of expansion between germanium (5.8 x 10-6 K-1) and sapphire (5 x 10-6 K-1) make the bonding of germanium to sapphire a reality. Germanium directly bonded to sapphire results in microvoid generation during post bond annealing. Inclusion of an interface layer such as silicon dioxide layer by plasma enhanced chemical vapour deposition, prior to bonding, results in a microvoid free bond interface after annealing. Grinding and polishing of the subsequent germanium layer has been achieved leaving a thick germanium on sapphire (GeOS) substrate. Submicron GeOS layers have also been achieved with hydrogen/helium co-implantation and layer transfer. Circular geometry transistors exhibiting a field effect mobility of 890 cm2/V s have been fabricated onto the thick germanium on sapphire layer.